1. Field of the Invention
The present invention relates to an organic electroluminescent display device and method for manufacturing the same. More particularly, the invention is directed to an organic electroluminescent display device and method for fabricating the same, in which corners of a lower (pixel) electrode are rounded off, thereby preventing contamination caused by outgassing and short-induced defects.
2. Description of the Related Art
With the development of active matrix organic light emitting devices (AMOLED) into flat panel display devices using organic electroluminescence devices (OELDs) and with application of AMOLEDs to mobile phones, great reduction in thickness, size and fabricating cost have been achieved.
FIG. 1A shows a planar structure of a conventional AMOLED having two transistors and a capacitor. FIG. 1B is a cross-sectional view taken along the line I-I of FIG. 1A.
Referring to FIG. 1B, the conventional AMOLED includes an emission region 110 and a non emission region 130. In the emission region 110, a lower electrode 131 (e.g., a pixel electrode), an organic emission layer 132 and an upper electrode 133 are formed. In the non-emission region 130 two thin film transistors (TFTS) and a capacitor are formed.
A buffer layer 140 is formed on a transparent insulating substrate 100 such as a glass substrate, and an amorphous silicon layer is deposited on the buffer layer to form a semiconductor layer 111. The semiconductor layer 111 is formed by performing a crystallization process after patterning the deposited amorphous silicon layer. Then, a gate insulating layer 150 is formed on the entire surface of the substrate. Thereafter, a metallic material for a gate electrode is deposited and patterned on the gate insulating layer 150 to form a gate 112 on the semiconductor layer 111. Additionally, a capacitor lower electrode 122 is simultaneously formed at this time. Upon formation of the gate 112 and the capacitor lower electrode 122, a gate line 102 of FIG. 1A is also formed.
Thereafter, source/drain regions 113 and 114 are formed by ion implantation of, for example, P or N type impurities, into the semiconductor layer 111.
Next, an interlayer insulating layer 160 is formed on the entire surface of the substrate. Then the interlayer insulating layer 160 and the gate insulating layer 150 are etched to expose portions of the source/drain regions 113 and 114, thereby forming contact holes 161 and 162 for source/drain electrodes.
Then, after a metallic material for the source/drain electrodes is deposited on the interlayer insulating layer 160, the source/drain electrodes 115 and 116 are formed to contact with the source/drain regions 113 and 114 through the contact holes 161 and 162. Then a capacitor upper electrode 126 is formed which extends from any one electrode, for example, the source electrode 115, of the source/drain electrodes 115 and 116; at the same time, a data line 104 and a power line 106 of FIG. 1A are also formed.
Thereafter, a passivation layer 170 is formed on the interlayer insulating layer 160. The passivation layer 170 is etched as to expose a portion of the other electrode, for example, the drain electrode 116, of the source/drain electrodes 115 and 116, thus forming a contact hole 171 for a pixel electrode.
Then, a transparent conductive layer is deposited on the passivation layer 170 and is patterned to form the lower electrode 131 contacting with the drain electrode 116 through the contact hole 171 for pixel electrode in the emission region 130.
After an insulating layer 180 is formed on the passivation layer 170, an opening 181 is formed to expose the lower electrode 131. An organic emission layer 132 is formed on a planarization layer 180 including the opening 181, and an upper electrode 133 is formed thereon.
In the conventional OLED, although the insulating layer 180 is similar to a pixel definition layer (PDL) defining the emission region, the PDL is commonly formed of an organic layer. However, a problem arises in that the organic emission layer 132 becomes contaminated due to outgassing. To address this problem, an organic light emitting display device may be formed without such pixel definition layer. However, another problem often experienced in conventional OLEDs formed without pixel definition layers is short-induced defects that generate a dark spot in their corresponding pixels.
For example, FIG. 2A shows an embodiment of the planar structure of an organic light emitting display device without a pixel definition layer, and FIG. 2B is a cross-sectional view taken along the line II-II of FIG. 2A.
A method for manufacturing the organic light emitting display device without such pixel definition layer is now explained with reference to FIGS. 2A and 2B.
Referring to FIGS. 2A and 2B, a thin film transistor and a capacitor are formed on a non emission region 220 in the same manner and structure as illustrated in FIGS. 1A and 1B. Then, a lower electrode 261 is formed by depositing a transparent conductive layer in the emission region on the entire surface of a substrate so as to contact source/drain electrodes formed in the non-emission region through a contact hole 255b for pixel electrode and patterning the same.
Now, steps for forming the lower electrode 261 are illustrated through FIGS. 2C to 2E. FIG. 2C is a perspective view showing the steps for forming the lower electrode 261, FIG. 2D is a plan view of the lower electrode 261, and FIG. 2E is a cross-sectional view taken along the line III-III of FIG. 2D.
Referring to FIGS. 2C to 2E, corners of upper and lower portions of the lower electrode 261 are formed in an angle shape. As shown in FIG. 2E, a length L2 of the lower portion of the lower electrode 261 is formed longer than a length L1 of the upper portion of the lower electrode 261. That is, the lower electrode 261 has a side slanted at a tapered angle.
An organic emission layer 262 is formed on the lower electrode 261. Then an upper electrode 263 made a metallic material is formed on the organic emission layer.
Upon the formation of the organic emission layer 262 on the lower electrode 261, a step is formed. However, in use, a short-induced defect may be generated due to an open edge phenomenon. Thus, in the case where the upper and lower portions of the transparent conductive layer are angled, the organic emission layer 262 often deteriorates at its corner portion to expose the lower electrode 261.
To address this problem, embodiments of the invention provide a lower pixel electrode having rounded corners.
Illustratively, FIG. 2F shows an enlarged view of an emission region upon the generation of a short-induced defect.